Contactless power transfer has been used in applications such as the non-intrusive charging of pacemaker batteries, the charging of hybrid vehicle batteries, etc. In such applications, inductive coupling is used exclusively so that a current is induced from a power station to a load. In such systems, the power transfer is exclusively accomplished by means of coupling magnetic flux of the power station and the load.
For example, road systems that would encourage the use of electric vehicles have been studied by states such as California. In such a system, inductively coupled flat coils are embedded in the roadway, or cables that are embedded in the roadway are energized, so that an induction coil of the vehicle receives induced current from the roadway coils to permit battery charging and/or even propulsion. Typically such a system requires that the flux collection surface of the buried coil and the vehicle maintain a distance within five centimeters of each other to provide sufficient power transfer by induction.
U.S. Pat. No. 5,608,771 to Steigerwald et al. discloses a contactless power transfer system, wherein power is transferred from a stationary supply to a rotational load via the use of a rotary transformer. This system eliminates the brush and slip ring arrangements. The coupling in this type of system is also inductive.
Another arrangement is the use of a clamp-on link around a primary conductor that does not physically contact the conductor. The transfer of power is still via induction.
In a separate field, that of security identification, there are identification tags for persons and vehicles (such as the EZ-Pass, Smart-Tag and Fast Lane automatic toll collection systems on parts of Interstate 95 and certain bridges in tunnels from Boston to Virginia) that do not provide power transfer, but are used in a form of wireless communication. The security tags and toll collection tags include both inductive-coupled and capacitive-coupled transponders. The prior art lacks a system for contactless power transfer that includes capacitive-coupled functionality of electric flux, in addition to the inductive coupling of magnetic flux.
It would be advantageous to provide a planar resonator for wireless power transfer that allows power transfer over a non-magnetic, non-conductive, galvanically-isolated volume (material). The resonant component exhibits the characteristics of an integrated inductor-capacitor-transformer.
In a first aspect of the invention, a planar resonator includes a coil arranged in a single spiral configuration. However, when used in a multiple spiral configuration, the capacitance between the spirals can be used for energy transfer, resulting in a combination of electric and magnetic energy transference across an IOET. In another aspect, the spirals can be arranged on opposite sides of each other. The connection a can be wireless, for example, so that a battery of a cellphone could be charged without physical wires connecting the cellphone to a charger.
Depending on the physical arrangement and/or the materials used, the planar resonator stores both electric and magnetic energy for the purpose or impedance matching or accomplishing soft-switching in an attached switching power electronic converter circuit, in addition to transferring power across the interface-of-energy-transfer (hereafter “IOET”) in either an electric or magnetic form, or both. The physical arrangement and/or materials used can permit transformer action with or without capacitive energy transfer, in addition to inductive energy storage, electrical (capacitive) energy storage or combinations thereof, such as magnetic transformer coupling with built-in LC resonant properties. The planar resonator does not necessarily use the IOET for energy transfer, for example, in a single coil configuration.
According to another aspect of the invention, an isolating coupling interface and a resonant tank are functionally integrated into a planar configuration for transferring power with isolation properties. The device may comprise two separable structures on either side of the IOET, such as, for example, a cellphone and its charger. Since there are no electrical contacts necessary at the IOET, the size of the entire charging circuit may be reduced while still complying with isolation specifications for safety standards such as IEC950. The physical structure may include a set of spiral coils on each side of the IOET, typically with each spiral being a conductor trace on a separate substrate, such as flex or printed circuit board (FR-4).
An advantage of the present invention is that it facilitates the use of wearable electronics. For example, flex circuits may be used so as to cause the surface of the coils to be flexible. In addition to the flexibility, the coils may be formed in any arbitrary shape to facilitate woven wire arranged in a fabric, or pads with embedded conductors that can be attached to clothes. In this way, for example, one could charge a radio, cellphone, and/or computer (just to name a few of the many wearable items) by bringing the device in close proximity to the fabric. Thus, implementation of the invention with wearable electronics could provide an interface between the wearable device(s) and external power sources. Digital or analog signals may also be transmitted across such interfaces to, for instance, up- or download digital information.
In another aspect of the invention, the IOET of the planar power resonator may have a thin and/or relatively flat top coil surface. In a wireless application, the IOET may be comprised of, for instance, (i) a non-conductive/dielectric film (for isolation) on the bottom of the top spiral(s), (ii) air; and (iii) a non-conductive/dielectric film (for isolation) on the top of the bottom spiral(s). The coils may be arranged in an upper and lower configuration substantially axially aligned. In addition, there can be an emulsifier at the bottom portion of an upper coil, with an air gap between the emulsifier and the top portion of the lower coil.
The spiral-shaped conductor may comprise pcb spiral-wound conductors. In addition, a battery charging circuit can be coupled to one of the first and second spiral-shaped conductors, and a load can be coupled to the other of the first and second spiral-shaped conductors. The coupling between battery charging circuit and the battery may comprise capacitive coupling and/or magnetic coupling, and wherein power is transferred by the coupling of an electric field and/or magnetic flux across the IOET.
According to an aspect of the present invention, a signal applied to the first spiral-shaped conductor can be transferred to the second spiral-shaped conductor by coupling of magnetic flux of the first and second spiral-shaped conductors across the IOET.
The first and second spiral-shaped conductors and the IOET are preferably integrated into a planar (flat/thin) structure.
The planar resonator may further comprise a third spiral-shaped conductor arranged in a bi-filar spiral configuration with the first spiral-shaped conductor on the top surface of the IOET, and/or a fourth spiral-shaped conductor arranged in a bi-filar spiral configuration with the second spiral-shaped conductor on the bottom surface of the IOET. It should be understood that a bi-filar top and single bottom, or single top and bi-filar bottom are alternative arrangements. Equivalent series or parallel resonator operation can be accomplished by the absence or presence, respectively, of galvanic connections between these two spirals.
The bi-filar spiral configuration on the top surface and bottom surface of the IOET can be therefore be arranged to form a parallel resonator, or a series resonator.
In addition, instead of a bi-filar configuration, a plurality of spiral-shaped conductors can be arranged in a multi-filar configuration on the respective top or bottom surface. The spiral-shaped conductors can be configured so the planar resonator comprises a parallel resonator, or a series resonator.
The first plurality and second plurality of spiral-shaped conductors may be configured so the planar resonator comprises a parallel resonator, or a series resonator. There can be an arrangement wherein each coil forms a capacitor plate. In this arrangement the planar resonator acts as an inductor and capacitor series.
A bi-filar arrangement can also be obtained by a second film of dielectric material that separates the two spirals that form the bi-filar arrangement on one side of the IOET. (I.e. the dielectric film is on top of top spiral; another spiral rests on top of this dielectric film. This dielectric film stores electric energy and forms the capacitive part of the resonator, where the inductive part is obtained from the self-coupling of the set of spirals either side of the dielectric film.
Instead of a bi-filar arrangement, where the spirals are wound in the same direction, one of the spirals may have an opposite winding direction. Thus, the two spirals in this case would not lie in the same physical plane. This advantage can be exploited when it is necessary or desirable to have a flexible circuit, or when it might be desirable to have several layers of coils to increase the magnetic and electric capabilities of the resonator. Each of the above arrangements exhibit transmission line properties, some with multiple resonant frequencies. Electrical behavior may further be modeled by a distributed network of equivalent electrical resistors, capacitors, inductors and coupled inductors. The values of the distributed elements and thus the electrical behavior of the structure at its terminals, including resonant frequencies, impedance, gain and phase are controllable by choice of material properties and the geometric configuration of the spirals and interfaces.